The present invention relates to a method of cutting sheet material with a cutting blade and, more particularly, relates to a method by which the relative motions of a cutting blade and sheet material are modified with scheduled supplemental motions to improve cutting accuracy. The method has particular utility in cutting layups of limp sheet material with automatically controlled cutting machines.
Automatically controlled cutting machines such as disclosed and described in U.S. Pat. Nos. 3,855,887 and 3,864,997 having the same assignee as the present invention have been known and used for some time for cutting various types of sheet material particularly limp sheet material such as fabrics, paper, cardboard, leather synthetics, rubber and others. Generally such automatically controlled machines derive information from a marker defining the contours or cutting paths to be followed. A marker is an array of closely packed pattern pieces positioned relative to one another in the same manner in which they are cut from the sheet material. In order to convert the marker information into machine commands, the cutting paths are reduced to point data by a digitizer, and then the digitized data is converted into basic or fundamental machine command signals which are received by the automatic machine and which guide a cutting blade or other cutting tool in the material along cutting paths corresponding to the patterns and contours in the marker. Alternatively, line followers or other instruments may track the patterns or contours in the marker and provide information which is converted into the fundamental machine commands.
A special technique for controlling the cutting blade as it advances along a cutting path in a layup of sheet material is disclosed in the above-referenced U.S. Pat. Nos. 3,855,887 and 3,864,997. In particular, a yawing technique comprised of rotating the cutting blade slightly out of a position tangent to the cutting path is utilized to control a reciprocating cutting blade as it advances along a cutting path in close proximity to adjacent cuts. The rotation is in a direction which orients the blade away from the previous, adjacent cut and prevents the blade from jumping into the cut near the point of tangency due to unbalanced lateral loading of the blade. In addition, the feed rate of the cutting blade may be reduced at the same time, especially with reciprocating cutting blades, in order to refine the cutting operation by increasing the number of cutting strokes per unit length of cutting path. The yaw and reduced feed rate commands are contained within the computer controlling the cutting machine, and are selectively drawn upon in accordance with previously recorded data.
Such special techniques for controlling the motions of a cutting blade cause the blade to track a desired cutting path with minimal error in spite of complex loading, particularly in multi-ply layups of sheet material. Stress and strain produced within the blade by the loading cause the blade to bend and deviate from a desired cutting path in spite of the accuracy with which servomechanisms or other positioning mechanisms locate the blade. Without special techniques, the deviations are often sufficient to produce cutting errors which are too significant to be ignored.
Several objects are achieved by the special techniques of controlling blade motions. First of all, cutting is carried out with greater accuracy and uniformity. It is highly desirable to have uniformity among pattern pieces which are cut from different layers of a multi-ply layup of sheet material because such uniformity enables pattern pieces to be used interchangeably. An item of upholstery or a garment can therefore be assembled with greater ease and more consistent quality.
Secondly, with greater assurance that the cutting blade will track a desired cutting path, pattern pieces may be more closely packed in the marker. Closer packing conserves material and since material is a significant factor in the cost of the finished product, the product can be manufactured at a lower cost.
It is a general object of the present invention to provide a method for establishing useful special cutting techniques and for utilizing those techniques when established to improve overall cutting performance.